The present invention is concerned with the field of valves and actuators and relates to a pneumatic actuator. More particularly, the present invention is an improved pneumatic actuator, which includes a rotary piston that reciprocates within a housing.
FIG. 1 shows a conventional pneumatic valve actuator which includes a toothed shaft 10, an actuating shaft 20 extending through the toothed shaft 10, two piston members 30 each having a rack member 301 engaged with the toothed shaft 10, and a plurality of springs 302 biasedly disposed between an inner side of a housing 40 and the piston members 30. In operation, the pneumatic valve actuator operates on the basis of cycles of air movement. At the beginning of a cycle air under pressure enters the interior of the housing 100 via two holes 41 to push the piston members 30 from a starting position away from each other to a fully separated position (as illustrated in FIG. 1) such that the toothed shaft 10 is rotated in a counter-clockwise direction by the movement of the two rack members 301 and the springs 302 are thereby compressed. By virtue of the rotation of the toothed shaft the actuating shaft 20 is also rotated. The rotation of the actuating shaft 20 is utilized for some other function (not shown). When the piston members 30 reach the fully separated position air entry into the housing is stopped, and the two holes 41 are opened to vent the housing at which time, the springs 302 push the piston members 30 back to the original starting position and thereby the toothed shaft 10, and correspondingly, shaft 20 are rotated in a clock-wise direction. When the piston members reach the starting position, one cycle will have been completed. During operation, the force of pressurized air in the housing 100 causes leakage at the positions where the toothed shaft 10 and/or the actuating shaft 20 extend through the housing 40 (not shown in FIG. 1). Depending upon the construction characteristics and materials used in the valve, as well as the amount of pressure, even after using such actuators for a short period of time leakage can occur. Furthermore, the interior surfaces of the housing 40 and contact and sliding surfaces of the rack members 301 must be manufactured precisely to ensure that the rack members 301 slide smoothly along the inner surfaces of the housing 40 all of which increases the cost of manufacturing.
Another commonly used pneumatic valve actuator is illustrated in FIGS. 2 and 3. The actuator is disposed between a return spring 7400 and a valve 7200 with a shaft 6200 extending through the return spring, the actuator and the valve so that when pressurized air is injected into the actuator, the shaft is rotated to operate the valve.
The actuator includes a casing, including an upper casing 6010, a lower casing 6020 and a vane member 6400 which is received between the upper and lower casing. The upper and lower casing are connected by bolts 6030 along flanges extending from each of the upper and lower casing wherein the lower casing has two passages 6800 defined therein so that pressurized air can be injected from the air pump and into the passages. The shaft rotatably extends through the upper casing and the lower casing and securely extends through the vane member. A seal member 6600 is disposed to the vane member so that the piston member is reciprocally moved within the casing by pressurized air entering the casing through the passages. The shaft is co-rotated with the vane member so as to control the actuator between an open and closed position. A return spring means 7400 including a spring coil 7600 is disposed above the actuator casing in accordance with a requirement to automatically return the shaft to its starting position once the pressurized air is stopped, thereby returning the vane member to its original position.
The seal member tends to become quickly worn out because the seal member slides along an inner surface of the casing whenever the piston moves. Furthermore, the inner surface of each of the upper and lower casing must be machined smooth to prolong the life of the seal. The return means including the coil spring and the machining of the inner surface of the casing results in the whole assembly being quite expensive.
The present invention avoids the above-noted problems of the prior art by providing an improved pneumatic actuator comprising a simpler, cost efficient piston, spring, and seal assembly.
Accordingly, the present invention provides a pneumatic actuator comprising a housing having an inner surface, a piston having an exterior surface and disposed within the housing, a shaft connected to piston, and a seal simultaneously engaging each of the exterior surface of the piston, the inner surface of the housing, and the shaft, and defining first and second chambers within the housing. The first chamber can be substantially isolated from the second chamber. The seal can further include aperture means for receiving the shaft. The exterior surface of the piston can be movable relative to the seal. The seal can immovably reside in a groove formed within the inner surface of the housing. Movement of the piston from a static condition to an operative condition can be effected by fluid pressure. The actuator can further comprise resilient means for biasing the piston towards a static condition. The resilient means can have a first end and a second end, the first end engaging an inner surface of the housing within the second chamber, and the second end engaging the piston, and could include a leaf spring. The actuator can be operatively connected to a valve to effect movement thereof.
In another aspect, the present invention provides a pneumatic valve actuator comprising a housing, a piston, moveable between a stable condition and an operative condition, a seal for effecting sealing between the piston and the housing, and defining first and second chambers within the housing, and resilient means disposed within the housing for biasing the piston towards a static condition. The first chamber can be substantially isolated from the second chamber. The resilient means has a first end and a second end, the first end engaging an inner surface of the housing within the second chamber, and the second end engaging the piston. The actuator can be operatively connected to a valve to effect movement thereof.
In yet another aspect, the present invention provides a pneumatic actuator comprising a housing, a piston having an exterior surface, means to introduce fluid pressure into the housing to effect movement of the piston, and a seal for effecting sealing between the piston and the housing, and defining a first chamber and a second chamber within the housing, the seal engaging the exterior surface of the piston in a substantially fluid tight arrangement in response to fluid pressure in the first chamber. The seal can have a surface exposed to fluid pressure within the first chamber, the fluid pressure acting upon the surface to effect a substantially fluid-tight engagement between the seal and the exterior surface of the piston. The surface of the seal is other than perpendicular relative to an axis defined by the exterior surface of the piston. The actuator can be operatively connected to a valve to effect movement thereof.
In a further aspect, the present invention provides a pneumatic valve actuator comprising a housing, a rotary piston having at least a top, a bottom and a peripheral wall, sealing means, wherein the sealing means is cooperatively arranged with the housing and the piston such that the sealing means is in contact with the top, bottom and peripheral wall of the piston and the housing and thereby defines a first and second chamber within the housing, means for effecting movement of at least a portion of the piston from the first chamber into the second chamber and back into the first chamber, such movement comprising one cycle of the piston, means for transferring movement of the piston to a further device, wherein the housing is comprised of two halves and the sealing means is securely received in a groove which is formed upon joining the halves of the housing, the groove defines a loop on an inside wall of the housing where the halves join, the sealing means comprising a single loop of sealing material, and wherein the sealing material is selected from the group comprising Viton, Buna N(trademark) or polyurethane.
According to a further aspect of the present invention there is a pneumatic valve actuator comprising a housing having a first half and a second half each half containing at least one passage defined therethrough and communicating with the interior and exterior of the housing, a groove defining a loop in an inner wall of the housing and formed when the halves are joined, a first and second hole defined perpendicularly through the housing, the first and second holes located in alignment with each other and communicating with the groove, a rotary piston having a top, a bottom, a peripheral wall connected between the top and the bottom, and at least one intermediate wall connected perpendicularly between the top, the bottom and the peripheral wall, and further having two engaging holes perpendicularly defined through the top and bottom, wherein the two engaging holes each are defined by a rectangular periphery and the actuating shaft has a rectangular cross section, a seal member securely received in the groove on the inner wall of the housing, two seal member holes defined through the seal member and located to communicate with the first hole and second hole wherein the sealing means is cooperatively arranged with the housing and the piston such that the sealing means is in contact with the exterior of the piston and the housing and thereby defines a first and second chamber within the housing, means for effecting movement of at least a portion of the piston from the first chamber into the second chamber and back into the first chamber, such movement comprising one cycle of the piston, an actuating shaft rotatably extending through the first hole, the two seal member holes, the two engaging holes and the second hole, wherein the rotary piston is fixedly connected to the actuating shaft, the actuating shaft imparting movement of the piston to a further device.
According to another aspect of the present invention, there is a pneumatic actuator comprising a housing having an inner surface, a piston having exterior and interior surfaces and disposed within the housing, the piston having a first position and a second position, whereby the piston is urged from the first position to the second position by fluid pressure, a shaft connected to the piston, and resilient spring having a first end and a second end, the first end abutting against the inner surface of the housing and the second end fixedly connected to the shaft, for urging the piston from the second position to the first position, wherein the first end comprises a roller disposed against the inner surface of the housing. The shaft includes lever arms for imparting kinetic energy from the piston to the spring means, the lever arms disposed against the interior surface of the piston. The shaft comprises a two-part construction, each part having a hub with a lever arm extending from the hub and each part rotatable about an axle. The axle is a two-part axle. The piston further includes opposing first and second interior surfaces having opposing first and second recesses respectively for retaining the two-part axle, and wherein each of the hubs includes throughbores for receiving the two-part axle therethrough. The two-part axle is spring-loaded by a spring means disposed between each part of the two-part axle for urging each part of the two-part axle against the first and second recesses.
According to a further aspect of the present invention there is a pneumatic actuator comprising a housing having an inner surface and defining a chamber, a piston having exterior and interior surfaces and disposed within the housing, the piston having a first position and a second position, whereby the piston is urged from the first position to the second position by fluid pressure, a shaft connected to the piston, a spring support member extending from the inner surface of the housing, resilient spring having a first end, and a second free end, the first end connected to the shaft, the second free end extending outwardly from the shaft and into the chamber, and the second free end being biassed against the spring support member. The first end of the resilient spring can be secured to the shaft.
Other advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.